PEEK Pipe Extrusion With Controlled Cooling for Low Residual Stress
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Solution Overview
Problem
Pipes made from fast-crystallizing polymers often exhibit significant differences in crystallinity across the wall, leading to residual hoop stress, which can cause premature failure and reduce their useful lifetime, especially under high pressure and external forces.
Innovation Solution
A pipe with a polymeric material comprising phenyl moieties, ether and/or thioether moieties, and optionally ketone and/or sulphone moieties, having a crystallinity half-life at 15°C above its glass transition temperature of less than 1000 seconds, and a residual stress of less than 5 MPa, achieved through controlled extrusion and cooling processes to maintain uniform crystallinity across the pipe wall.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If water quenching is used to cool the extruded pipe, then production efficiency is improved, but residual hoop stress increases due to non-uniform crystallinity
Solution Approach 1:
The patent changes the cooling parameter from rapid water quenching to controlled cooling at a rate of 0.1-10°C per minute. This parameter change allows uniform crystallinity development throughout the pipe wall while maintaining production efficiency, resolving the contradiction between fast production and low residual stress.
Solution Approach 2:
The patent applies a preliminary action by maintaining the extruded pipe at a temperature above its glass transition temperature during extrusion, then controlling the cooling rate from this pre-heated state. This preliminary temperature maintenance ensures uniform crystallization throughout the pipe wall before cooling begins, preventing residual stress formation.
2Productivity
If rapid quenching is applied to the extruded pipe, then manufacturing speed is improved, but crystallinity uniformity deteriorates
Solution Approach 1:
The patent changes the cooling parameter from rapid quenching to controlled cooling at 0.1-10°C per minute. This parameter change provides sufficient time for uniform crystallinity to develop throughout the pipe wall while maintaining acceptable manufacturing speed, resolving the contradiction between speed and composition uniformity.
3Ease of manufacture
If conventional extrusion and water quenching are used, then production cost is reduced, but pipe lifetime is shortened due to high residual stress
Solution Approach 1:
The patent changes the cooling rate parameter to 0.1-10°C per minute, which reduces residual hoop stress to below 5 MPa. This parameter change extends pipe lifetime by reducing stress-related failures while keeping the process simple and cost-effective, resolving the contradiction between production cost and service life.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution results in pipes with reduced residual stress, enhanced mechanical properties, and extended lifetime by minimizing differences in crystallinity and hoop stress, thereby improving their resistance to failure and performance under operational stresses.
Implementation Method 1
for fast crystallizing polymers and/or polymers having a relatively high glass transition temperature such methods may produce pipes which have significant differences in crystallinity from the outside to the inside of the pipe wall
Implementation Method 2
water quenching the extruded pipe, for example by directing it into a cool water bath and/or by spraying cool water on its outside
Implementation Method 3
Such residual stress is a consequence of the thermal contraction of the melt being restricted during non-uniform solidification which freezes in a strain
Data Source
AI summary
A polyetheretherketone pipe of length greater than 250 meters and a residual stress of less than 5 MPa may be made using a calibrator device 2 which includes a cone shaped opening 6 arranged to receive a molten extruded pipe shaped polymer. Attached to the front member 4 is a vacuum plate 14a and successive vacuum plates 14b-14h are attached to one another to define an array of vacuum plates, the vacuum plates being arranged to allow a vacuum to be applied to a pipe precursor passing through opening 16. The vacuum plates 14 also include temperature control means for heating or cooling the plates and therefore heating or cooling a pipe precursor passing through the openings. With a vacuum applied to opening 6, 16 and heating/cooling the plates, an extruded hot plastics pipe is inserted into calibrator 2 via opening 6 and conveyed through opening 16 in plates 14, whereupon it is urged by the vacuum against the cylindrical surface defined by plates 14 to maintain its shape and the temperature of each plate is controlled to control the rate of cooling of the pipe precursor passing through. The pipe may be cooled at a relatively slow rate so that a pipe made from a relatively fast crystallising polymer crystalises and the crystallinity of the pipe along its extent and throughout its thickness is substantially constant.